The present invention relates to a work pick-up apparatus incorporating a visual sensor such as an ITV camera and capable of controlling an operation for picking up a work in accordance with work position information concerning the position of the work derived from the visual sensor. More particularly, the present invention is concerned with a work pick-up control apparatus which conducts a control such that a specific work is picked up out of a plurality of works stored in a magazine, a pallet or a similar container (referred to simply as "pallet" hereinafter).
In a known automatic assembly system incorporating a robot for handling a plurality of parts or works, a pallet is provided with guide surfaces conforming with the configurations of the works so that the works are set with high positional accuracy, and the works are arranged on the pallet in the form of a matrix to enable the robot to store data concerning the positions of the works. The assembly system picks up a selected work out of the pallet and mounts the same on a predetermined portion of an object which is being assembled.
Referring to FIG. 2A, a work 1 as an example of works handled by a known assembly system is provided with guide holes 1a and 1b. Numeral 1c denotes the gravity center of the work. FIG. 2B shows a plurality of works 1 arranged on a pallet 2. Although not exclusive, the pallet 2 is provided with recesses arranged in the form of a matrix having four lines and four columns so as to receive 4.times.4 works. Each of the recess is provided with guide pins 2a, 2b projecting upward from the bottom thereof. Each work 1 can be precisely fixed in each recess by virtue of mutual engagement between these guide pins 2a, 2b and the guide holes 1a, 1b formed in the work 1. FIG. 2C is a sectional view taken along the line X--X of FIG. 2B, showing two of such works 1 fixed in the respective recesses by means of the pins 2a, 2b. Hitherto, it has been necessary to locate the pallet 2 with respect to the robot at a high precision by, for example, clamping the pallet 2.
FIG. 3 shows the relationship between the work position and the robot coordinate. In general, the works are arranged on the pallet at constant pitches both in longitudinal and transverse directions, e.g., at a pitch a in X-direction and at a pitch b in Y-direction. The robot stores coordinate data of all points or coordinates of three corner points, e.g., points 3, 4 and 5 shown in FIG. 3, and computes the coordinates of an aimed point so as to move to a position where it can pick up the object work.
The described system incorporating a pallet has the following problems. The pallet is required to have high precision in order to enable the robot to pick up the object work without fail. Such a precise pallet is expensive. In addition, it is necessary to employ suitable means or device capable of locating the pallet with respect to the robot at a high precision. For these reasons, the cost of the whole assembly system is raised uneconomically.
In recent years, a system has been proposed as in, for example, Japanese Patent Application Laid-Open Nos. 60-56884, 60-123974 and 62-147024, in which a robot operates in accordance with position data obtained through an image processing operation conducted on outputs from a visual sensor.
According to Japanese Patent Application Laid-Open No. 62-147024, a parts feeder feeds parts one by one into the field of vision of a camera used as a visual sensor to enable the camera recognize the positions of these parts so that pick-up of the part is conducted in accordance with the data derived from the camera. It is true that this system employing a visual sensor enables a high accuracy of gripping of parts.
In the arts shown in Japanese Patent Application Laid-Open Nos. 60-56884 and 60-123974, an image is formed with a plurality of works positioned in the field of vision, and an approximate position of an object work is determined from this image, followed by recognition of the exact pick-up position from an enlarged image which is formed to cover an area around the object work.
Unfortunately, however, the system of 62-147024 cannot be applied to the field to which the present invention pertains, i.e., the field in which a specific part has to be picked up out of a plurality of parts arranged on a pallet, since this known system requires that parts are brought into the field of vision of a camera. Namely, when the known system is applied to gripping of a selected one of a plurality of works on a pallet, a plurality of works may be simultaneously taken into the image pick-up area of the visual sensor, depending on the size of the works. In such a case, it is difficult to determine which one of the recognized works has to be picked up.
The arts shown in Japanese Patent Application Laid-Open Nos. 60-56884 and 60-123974 require a preliminary step in which the visual system recognizes the rough positions of independent works from the image which contains the images of a plurality of works. This preliminary operation is time-consuming and causes an impediment to improvement in the processing speed of the whole system.